1-Phenylazulene (I) and 2-phenylazulene (II) were synthesized from the troponoid compound. 3-Phenyl-(III) and 3-benzoyl-2H-cyclohepta[b]furan-2-ones (IV) were prepared by the reaction of 2-chlorotropone with ethyl phenylacetate and with ethyl benzoylacetate respectively. The reactions of III with malononitrile or ethyl cyanoacetate gave 1-phenylazulene derivatives, from which I was derived. On the other hand, the reactions of IV with ethyl cyanoacetate or diethyl malonate gave 2-phenylazulene derivatives, from which II was derived.
7-Isopropyl-2,4-dimethylazulene (Se-guaiazulene) (I) was synthesized from 4-isopropyl-7-methyltropolone (II), which had itself been derived from 4-isopropyltropolone. The tropolone, II, was then converted to 3-acetyl-5-isopropyl-8-methyl-2H-cyclohepta[b]furan-2-one (VI) via the p-tolylsulfonyloxytropone derivative derived from II. The application of the azulene synthesis to VI gave 3-cyano-7-isopropyl-2,4-dimethylazulene-1-carboxylic acid (VII), from which I was obtained by the removal of the carboxyl and cyano groups.
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